1. Field of the Invention
The present invention relates to an etching technique, and particularly relates to an etching technique that employs radicals. Specifically, the present invention relates to an etching apparatus that performs etching processing of a natural oxide film formed for example on the surface of a semiconductor wafer in a vacuum, and to a dry etching method.
Priority is claimed on Japanese Patent Applications Nos. 2004-5212, 2004-5213, 2004-5218, and 2004-5220 filed on Jan. 13, 2004, the contents of which are incorporated herein by reference.
2. Description of Related Art
In the process of manufacturing a semiconductor device, it is necessary to remove a natural oxide film formed for example, on the substrate surface of a contact hole bottom part of a semiconductor wafer.
Conventionally, wet etching that uses HF is performed in order to remove the oxide film on the semiconductor surface. However, a dry etching method that uses radicals is recently drawing attention as a technique for removing in particular a natural oxide film on the semiconductor surface (for example, see Japanese Unexamined Patent Application, First Publication No. Hei. 10-335316).
In this etching method, reactive gas and radicals are introduced into the vacuum atmosphere of a reaction chamber and reacted with the natural oxide film on the substrate surface, and a reaction product is thermally decomposed, and the gas produced is removed by evacuation.
For example, when an etching object formed of a silicon oxide film formed on a surface of a silicon substrate is etched with a dry etching method, the substrate is first disposed in a reaction chamber, and after a vacuum atmosphere is formed in the reaction chamber, an intermediate product that reacts with the etching object is produced in the reaction chamber.
For example, when radicals of hydrogen gas and a reactive gas such as fluorine gas are supplied to the reaction chamber, the reactive gas is reduced, and an intermediate product such as NHxFy (x and y are optional integers) is produced.
The intermediate product reacts with the etching object on the surface of the substrate, and a reaction product is produced. Then as heat is applied to the substrate, the reaction product is thermally decomposed, and becomes a pyrolysis gas such as NH3 gas, HF gas and SiF4 gas and vaporizes. As a result, the etching object is removed from the substrate surface.
According to the dry etching method, the silicon oxide film can be removed by etching in the vacuum atmosphere, and hence the silicon substrate is not contaminated by moisture and oxygen in the air.
A reaction like this is sometimes performed by sheet processing or by batch processing in which a number of substrates are carried into the reaction chamber and are subjected to etching processing at the same time (see Japanese Unexamined Patent Application, First Publication Nos. 2001-284307 and 2003-124172).
However, there is a problem in a conventional technique like this in that it is difficult to ensure the in-plane uniformity after processing.
Particularly, when a number of semiconductor wafers are processed at the same time, there is a problem in that the in-plane uniformity varies according to the position of the semiconductor wafer in the vacuum processing tank. Specifically, there is a problem in that the reaction rate varies among a number of substrates disposed in the reaction chamber depending on their positions relative to the radical introduction port and to the gas introduction port, and the etching amount around the periphery and the center of the substrate varies on a single substrate
Moreover, in the conventional dry etching method, particles sometimes adhere to the inner wall of the reaction chamber in the etching process. The device thus needs to be stopped and the particles that adhere to the inner wall of the reaction chamber regularly removed, and the removal operation is complex.
The present invention has been created in order to solve the above mentioned problems of the conventional technique, and its first object is to provide an etching apparatus that allows fast reaction rate and high speed processing of a number of etching objects, and that can improve the in-plane uniformity of the processing object after processing. A second object is to provide a technique that prevents the occurrence of particles and that can remove particles without stopping the apparatus.